The second question:

The third question:

The fourth question:

This part of the extended materials mainly investigates the knowledge points of stress diagram:

Separate the studied component from the objects around it, and express all external forces acting on it. The sketch drawn in this way to show the force of an object is the stress diagram.

Determine the research object. Select the research object according to the problem studied. The research object can be a single object or a combination of multiple objects. Separate the object to be studied from the relationship of the surrounding objects and draw its diagram separately. This method is called taking the separated body, and the drawing is called the separated body diagram.

Draw the main force on the object under study. According to the type of constraint, draw the corresponding constraint reaction correctly. Never speculate on the direction of restraining reaction simply by subjective speculation or simply by the direction of main force.